This invention relates to a method of controlling a vehicle hydraulic brake system provided with a hydraulic pressure source for producing brake hydraulic pressure.
In recent years, in order to achieve sophisticated vehicle behavior control and a light feeling of brake operation, as described e.g. in Japanese patent publication 2590825, a vehicle hydraulic brake system is employed in which a hydraulic pressure source for producing brake hydraulic pressure is provided and a driving device for the hydraulic pressure source is actuated based on a detection signal from a brake operating force detecting means for detecting the operating force applied to a brake operating member.
E.g. in a hydraulic pressure source-driven type brake system described in Japanese patent application 11-332660 by the present applicant, a brake fluid replenish passage communicating a master cylinder and wheel cylinders with each other, and an on-off valve and a check valve for preventing reverse flow from the wheel cylinder side toward the master cylinder are mounted in the replenish passage to replenish brake fluid from the master cylinder toward the wheel cylinders if the amount of brake fluid from the hydraulic pressure source is insufficient.
In a brake system provided with such a brake fluid replenish passage, the brake hydraulic pressure in the wheel cylinders and the hydraulic pressure in the master cylinder are detected, and the on-off valve in the replenish passage is opened when the pressure difference between the master cylinder hydraulic pressure and the brake hydraulic pressure exceeds a predetermined value, to replenish brake fluid from the master cylinder side to the wheel cylinders. This replenish passage is opened in the initial period of brake operation, in which due to the fact that the consumed fluid amount in the wheel cylinders is large, a hydraulic pressure difference between the master cylinder hydraulic pressure and the brake hydraulic pressure tends to occur.
If brake hydraulic pressure is produced only by the hydraulic pressure source by closing the replenish passage, using the pressure difference between the master cylinder hydraulic pressure and the brake hydraulic pressure as an input signal for control, the driving force by the driving device for the hydraulic pressure source is PID-controlled.
In such a hydraulic pressure source-driven type brake system, the master cylinder for producing hydraulic pressure according to the operating force applied to the brake operating member is in communication with wheel cylinders through the on-off valve by way of the so-called master cylinder passage. If the hydraulic pressure source is not operating normally, the hydraulic pressure in the master cylinder is transmitted as brake hydraulic pressure by opening the on-off valve to provide a failsafe function.
In the hydraulic pressure source-driven type brake system provided with such a brake fluid replenish passage, since the on-off valve in the replenish passage is opened when a large hydraulic pressure difference is produced between the master cylinder hydraulic pressure and the brake hydraulic pressure, water-hammering sound tends to be produced due to a sharp inflow of brake fluid through the replenish passage toward the wheel cylinder side, or vibration due to such water-hammering is transmitted to the brake pedal as the brake operating member through the master cylinder, thus worsening the pedal feeling.
An object of this invention is to provide a method of controlling a hydraulic pressure source-driven type vehicle hydraulic brake system in which water hammering or worsening of the pedal feeling will not happen when brake liquid is replenished through the replenish passage.
According to this invention, there is provided a method of controlling a vehicle hydraulic brake system comprising a brake operating member, a master cylinder for producing hydraulic pressure corresponding to a brake operating force applied to the brake operating member, a wheel cylinder, a hydraulic pressure source for producing brake hydraulic pressure in the wheel cylinder, a driving device for the hydraulic pressure source, a fluid passage for bringing the hydraulic pressure source into communication with the wheel cylinder, a fluid replenish passage for bringing the master cylinder and the wheel cylinder into communication with each other, an on-off valve and a check valve provided in the fluid replenish passage, the check valve preventing a reverse flow from the wheel cylinder toward the master cylinder, a brake operating force detecting means for detecting the brake operating force, a brake hydraulic pressure detecting means for detecting the brake hydraulic pressure in the wheel cylinder, and a master cylinder hydraulic pressure detecting means for detecting the hydraulic pressure in the master cylinder, the driving device for the hydraulic pressure source and the on-off valve in the fluid replenish passage being actuated based on signals from the brake operating force detecting means, the brake hydraulic pressure detecting means and the master cylinder hydraulic pressure detecting means, wherein when the brake operating force detecting means detects a predetermined brake operating force, the on-off valve in the fluid replenish passage is opened and the driving device for the hydraulic pressure source is actuated at full driving force, and upon detection of the fact that the difference between the master cylinder hydraulic pressure and the brake hydraulic pressure, which are detected by the master cylinder hydraulic pressure detecting means and the brake hydraulic pressure detecting means, respectively, has entered a predetermined range, the on-off valve in the fluid replenish passage is closed and the driving device for the hydraulic pressure source is actuated at a driving force corresponding to the difference between the master cylinder hydraulic pressure and the brake hydraulic pressure.
By actuating the driving device for the hydraulic pressure source at its full driving force with the on-off valve in the brake liquid replenish passage opened in an initial stage of brake operation in which the difference between the master cylinder hydraulic pressure and the brake hydraulic pressure is small but the brake operating force has reached a predetermined value, the occurrence of water hammering due to a sharp inflow of brake liquid to the wheel cylinder side from the replenish passage is prevented.
Also, when the brake hydraulic pressure has increased and the hydraulic pressure difference from the master cylinder hydraulic pressure has entered a predetermined range, the on-off valve in the replenish passage is closed to return to normal control mode in which the driving force of the driving device for the hydraulic pressure source is controlled so as to correspond to the difference between the master cylinder hydraulic pressure and the brake hydraulic pressure.
This control method of a vehicle hydraulic brake system can be applied to a brake system in which a master cylinder passage for bringing the master cylinder and the wheel cylinder into communication with each other through an on-off valve is provided, and the on-off valve in the master cylinder passage is selectively opened and closed to transmit the hydraulic pressure produced in the master cylinder to the wheel cylinder.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: